1. Field of the Invention
The present invention relates to a video signal combining system in which first component video signals representing a trichromatic composite foreground scene and backing picture and second component video signals representing a trichromatic background scene picture are combined electronically to produce output component video signals representing a resulting combined picture resulting from the replacement of the backing by the background scene in the trichromatic composite picture. The combining system comprises output means for combining, i.e. inserting a picture issued from the foreground scene in the background scene in terms of colors differences in the foreground scene and the backing.
2. Description of the Prior Art
In the known combining systems, such as those disclosed in the U.S. Pat. Nos. 4,292,649, 3,778,542, 4,007,487, the published German Patent Application 2,749,154 and the published French Patent Application 2,128,156, the component video signals in said picture resulting from the foreground scene are obtained either directly from corresponding component video signals representing the foreground scene, via respective attenuators sometimes variable, or from at least one linear combination of component video signals representing the foreground scene. The known systems differentiate between the generally saturated color of the backing and the foreground scene colors so as to provide a gain controlling signal intended for distinguishing the backing from the foreground scene with a view to doing away with the backing and replacing the backing by the background scene.
For various reasons, particularly operational ease, the color in the backing which is the back-cloth to the foreground scene or object is highly saturated. In the very large majority of cases, blue is adopted. The component video signals representing the composite picture made up the foreground scene and the backing are delivered by a film camera on a deck where the foreground scene or object is positioned in front of a blue panel at the back of a studio and moves on a blue floor. The overall lighting must be such that a very regular backing color may be achieved. However, considerable reflected and diffused light occurs stemming from the panel and the floor. This light has a dominance of blue and gives rise in the foreground scene or object to, on the one hand, numerous blue reflections which detract from the natural aspect of the real colors in the foreground scene picture and, on the other hand, an edging which becomes more marked especially around the hair of a person in the foreground. The edging can again appear after combination in the foreground scene and background scene transition. A bluish transparency analogous to the edging mentioned above also appears when the foreground scene contains transparent objects, whatever the known combining system is used.